Choose the correct sequence of steps involved in `C_(4)` cycle.

Options

A. `CO_(2)` fixation ` to ` Regeneration ` to` Transport
B. `CO_(2)` fixation ` to ` Recorboxylation `to ` Decarboxylation
C. Transport ` to ` Regeneration ` to CO_(2` fixation
D. `CO_(2)` fixation ` to ` Transport ` to ` Decarboxylation

Answer

### Step-by-Step Solution for the C4 Cycle

1. **Carbon Dioxide Fixation**:
- The process begins when atmospheric carbon dioxide enters the mesophyll cells of C4 plants.
- In the mesophyll cells, carbon dioxide is fixed by the enzyme phosphoenolpyruvate carboxylase (PEPcase).
- This reaction converts phosphoenolpyruvate (PEP) into a 4-carbon compound, specifically oxaloacetic acid (OAA), which is the first stable product of carbon fixation.

2. **Formation of Other 4-Carbon Acids**:
- The oxaloacetic acid can be converted into other 4-carbon acids, such as malate or aspartate, depending on the specific C4 plant.

3. **Transport to Bundle Sheath Cells**:
- The 4-carbon acids are then transported from the mesophyll cells to the bundle sheath cells. This transport is essential for the next step in the cycle.

4. **Decarboxylation**:
- In the bundle sheath cells, the 4-carbon acids undergo decarboxylation, a process where one carbon is removed, releasing carbon dioxide.
- This reaction is facilitated by the enzyme ribulose bisphosphate carboxylase/oxygenase (Rubisco), which is present in the bundle sheath cells.
- The decarboxylation results in the formation of a 3-carbon compound (C3 acid), which can enter the Calvin cycle.

5. **Regeneration and Entry into the Calvin Cycle**:
- The C3 acid produced from decarboxylation is then transported back to the mesophyll cells.
- Here, it enters the Calvin cycle, completing the C4 cycle and allowing for the regeneration of the starting materials.

### Correct Sequence of Steps:
1. Carbon Dioxide Fixation
2. Formation of Other 4-Carbon Acids
3. Transport to Bundle Sheath Cells
4. Decarboxylation
5. Regeneration and Entry into the Calvin Cycle